The invention relates to a projection screen of a display device.
A rear projection television includes, for example, a projection type cathode ray tube (CRT) in which an image is formed. The formed image is projected via a projection lens on a rear projection screen. The rear projection screen provides a surface on which a final image is displayed for viewing. The rear projection screen redirects a diverging cone of light from the projection lens into a limited range of directions encompassing the locations of intended viewers, thereby providing a gain in image brightness. The rear projection screen also reduces reflections of ambient light that lower the contrast of the displayed image.
Rear projection screens generally include a Fresnel lens component for directing the light and a separate, lenticular lens component for producing the angular spreading of the light. The Fresnel screen component functions as a single large field lens that collects light from the projector and redirects the light so that it reaches the lenticular screen component approximately collimated. Therefore, the focal length of the Fresnel lens is determined by the requirement for collimated light and the optical distance to the projector. The Fresnel screen component can be formed from a sheet of clear optical material and is placed in contact with the projector side of the separate lenticular screen component.
Rear projection screens can be classified by the primary way that is used to spread the light after it has been redirected by the Fresnel lens component. The three categories are diffusive, refractive, and reflective/refractive. Diffusive structures consist of random patterns of small surface features and/or lightscattering particles distributed in the volume of the light-spreading lenticular lens. Refractive structures are formed of small lens like surface features that are carefully specified, and/or replicated in one or two dimensions at a well-defined pitch. Such lenticular arrays introduce a periodic spatial sampling of the projected image that can, disadvantageously, form moire beats with the projected pixels or with the Fresnel lens structure.
A typical lenticular screen component of a rear projection display has lenticular elements formed on a viewer surface. Identical lenticular elements cover the entire lenticular screen component and are repeated horizontally at a constant displacement. The lenticular elements vary in height only in a horizontal direction across the screen; there is no variation along the vertical direction through any given horizontal location. A given lenticle or lenticular element linearly spans the entire height of the lenticular screen component, without variation, from the top edge to the bottom edge. A given lenticular element has a pair of reflective sides and a lens section between the sides. The lenticular element changes the light direction by a combination of reflection and refraction. Reflectance occurs primarily at the sides of the lenticular elements that are reflective. Refraction takes place at the lens section where the light exits toward the viewer.
A lenticular lens component of a projection screen, embodying an inventive feature, includes lenticular elements. Each lenticular element extends in a vertical or a height direction and repeats in a horizontal or a width direction to form a plane defining a first axis normal to the plane. The given lenticular element includes a pair of reflective side portions and a refractive tip portion interposed between the side portions. One of the pair of side portions forms at a joint between the one side portion and a side portion of an adjacent lenticular element a sloped region at an angle in a range between 5 and 15 degrees with respect to the first axis. The one side portion is covered with a reflective coating in at least a region of the one side portion that includes the joint. The pair of reflective side portions reflects light rays incoming from a projector towards the refractive tip portion for refracting the reflected light rays via a surface of the refractive tip portion facing a viewer. Each refracted light ray is refracted by a convex surface of the refractive tip portion.
A trapping structure for ambient light is provided between the lenticular elements. Scattering structures are provided on the projector side surface (and/or within the interior of the volume).
A lenticular lens of a projection screen, embodying an inventive feature, includes a plurality of lenticular elements. Each lenticular element extends in a first direction and repeated in a second direction to form a plane defining a first axis normal to the plane. A given lenticular element includes a refractive tip portion and a pair of reflective side portions. The side portions have the refractive tip portion interposed between a pair of end edges thereof, respectively. At least one of the pair of side portions has a joining edge in common with a side portion of an adjacent lenticular element and has a sloped region that includes the common joining edge. The sloped region forms an angle smaller than 15 degrees with respect to the first axis. The one side portion is covered with a reflective coating at least in the sloped region that includes the common joining edge. The pair of reflective side portions reflect light rays incoming from a projector towards the refractive tip portion for refracting the reflected light rays via a surface of the refractive tip portion facing a viewer. Each refracted light ray from the tip portion is refracted by a convex surface.